Beryllium products and method



United States Patent 7 Int. Cl. B21c 23/24; B 21b 45/00; 1323!: 31/02US. Cl. 72-47 14 Claims This invention relates to finished andsemi-finished products of beryllium and alloys of beryllium and it is animprovement in the method for the processing of same.

A number of new applications and use have recently been found forberyllium such as for parts embodied in aircraft and space vehicles andin cryogenics such as cold generators. In such applications as inaircraft engines and space ships, use is limited to temperatures lessthan 500 C. and efforts are being made for improvement in the propertiesof the products, and particularly in their surface portions, to expandtheir range of use.

The following are given by way of illustration, but not by way oflimitation, of some of the more important of the properties sought to beimproved, namely: the two dimensional ductility of semi-finishedproducts, espe cially when in thin cross-section; resistance to shock,such as initiated by outside particles; resistance to corrosion invarious atmospheres and at extremely high temperatures; resistance toabrasion; resistance to friction between moving parts; mechanicalbonding thereto as by diffusion of other materials in operation, such asbrazing; bonding; and good electrical conductivity, amongst others.

Beryllium has not gained full acceptance because of its sensitivitytowards notching and such after effects as loss of ductility,propagation of cracks and the like. It is also faced by the problem ofinter-crystalline corrosion, high susceptibility to diffusion of othermetals and gases, and toxicity of dusts released by the beryllium duringprocessing.

It is an object of this invention to provide a process which overcomes anumber of the deficiencies of beryllium and products formed thereof andit is a related object to provide beryllium and a method and means forprocessing same to improve upon such deficiencies as notchingsensitivity, inter-crystalline corrosion, easy diffusibility of othermetals and gases, and the release of toxic dusts.

An important concept of this invention resides in the coating of theberyllium part with at least one layer of at least one plastic metal,such as aluminum, alloys of aluminum, magnesium, zinc and antimony.

The beryllium can be coated with one or several layers of one or anumber of the plastic metals by mechanical transformation in atemperature range which is compatible with the ductility of theberyllium and in which the inter-metallic diffusion can be controlled.By way of illustration, but not by way of limitation, the desired metalcoating can be achieved by such mechanical transformation as flattening,rolling, drawing, spinning and hammering, with the coating being formedat a temperature below 620" C. and preferably at a temperature withinthe range of 300-400 C.

It is possible to plate the beryllium to provide a coating of aluminumor an alloy of aluminum or of magnesium, zinc or antimony. It is alsopossible to apply the coating material in a multi-layered sandwich.Aluminum is preferred as the coating metal because it does not formbrittle compounds with beryllium.

The use of pure beryllium or alloys of beryllium which has [been castrather than fritted and has a good ductility at a wide temperature rangerequires the use of a plating temperature preferably within the range ofBOO-400 C.

From a practical standpoint, the temperature range which can be used ismuch wider. The lower limit is more or less dictated by the ductility ofthe beryllium which permits the transformation sought to be achieved. itis influenced also by the purity and the structure of the materialhandled such that it becomes possible to achieve transformation at roomtemperature.

The upper limit corresponds to the melting point or the temperature ofirreversible transformation of the plating metal. It is also influencedby the melting point temperature of the eutectic that is formed betweenthe base metal and the plating metal. For example, the upper limit is atemperature within the range of 600-620 C for pure aluminum, 550aluminum, 380400 antimony.

The invention will be described with reference to the use of acommercial grade of aluminum having a purity of 99.5%. The techniquewill be the same for others of the plastic metals with some slightmodification depending upon the particular metal, all of which are wellwithin the skill of the art.

The starting material will comprise a sheet of beryllium prepared from acast ingot by hot transformation in an inert atmosphere, such as byspinning or forging, followed by transformation at a lower temperature,without surface protection, to achieve a reduction by cold working of50l00%.

The first transformation breaks the coarse structure of the ingot andthe second improves the surface characteristics and provides additionalrefining.

While in this stage, the beryllium sheet can 'be subjected to varioustypes of mechanical or thermal processing, such as planing or sanding.In all such instances, the laminated surface is of a rather good qualityso that deep surface treatment will not be required.

The intermediate product is cut to the desired dimensions and is pickledin a bath of HNO +H F for removal of the layer of oxide and othersurface impurities. It is then introduced into a jacket in the form of asheet of aluminum which is folded about the product in which thealuminum sheet has previously been degreased and brushed.

The combination is preheated in an electric furnace having a temperaturewithin the range of 400-600 C. and preferably about 600 C. with the heatarising from the bottom of the furnace. The preheating temperature is atleast equal to the transformation temperature with the differences beingaccounted for by the temperature of the tools and the time for handling.After 15 minutes, the sandwich of beryllium and aluminum is removed fromthe furnace and is rapidly transferred to between heated rollers of arolling mill. The speed of rolling is 10-20 meters per minute with areduction of 10-15% being taken with each pass followed by reheating to600 C. for 5 minutes.

A reduction of at least 50% in cross-section is desired to achieve agood plating operation but a reduction as high as can be employed. Verythorough cold working can be achieved if the beryllium is first annealedbut this is not essential to obtain good plating.

After the rolling reduction, the assembly is slowly cooled, preferablywhile enclosed in an inorganic insulator to minimize the rate ofcooling. Thereafter, the product can be cut and machined without thenecessity to take other precautions except for the use of sufiicientexhaust for the removal of chips which might fall from the product. Thechipping off of sharp edges occurs only to a small extent.

Thermal treatments may be employed to overcome the stresses introducedand to improve the plasticity of the C. for most of the alloys of C. forzinc and 580-600 C. for

base metal. For this purpose, the plated metal is heated to atemperature which varies somewhat in proportion to time such as 550 C.for 500 hours, 575 C. for 200 hours, or 600 C. for 100 hours. Thesetreatments, which should be carefully controlled, will tend to widen orexpand the beryllium-diffusion layer by a substantial amount.

The following examples are given by way of further illustrations, butnot by Way of limitation, of the practice of this invention:

Example 1 Two layers of 99.5% aluminum are provided on the oppositesides of a sheet of cast beryllium to provide a composite thickness of 4mm., 80% of which is the cast beryllium sheet. The composite is hardenedby hammering or forging to effect a 50% reduction in cross-section afterwhich the composite is given a first anneal at 500 C. The annealed sheetis again forged to effect a reduction in thickness of 140% whereby thefinal thickness of the composite sheet is reduced to 1.15 mm.

The first anneal is intended to restore the ductility, as measured by a40 bend on a punch having a 5 mm. radius, before proceeding with thefurther reduction step.

Depending upon the use, the processed sheet can be employed in the stateresulting from the final working or it can be annealed at a temperatureof about 600 C.

Example 2 A composite sheet is formed of two sheets of cast berylliuminterleaved between three layers of aluminum to give a total thicknessof 3 mm.

The following table sets forth the mechanical characteristics of thecomposite in traction or after a rolling reduction of 50%:

Elastic Breaking Elongalimit, loa tion, kgJrnm. kgJmrn. percent Roughrolled composite 24 24v 8 1. 3 Composite annealed 48 hrs. at 600 21. 12.6 Composite annealed 100 hrs. at 600 Example 3 Plating of berylliumwith alloys of aluminum, in accordance with the practice of thisinvention, makes it possible to improve a number of the properties ofthe composite that is formed, such as mechanical strength and corrosionresistance. Aluminum-magnesium alloys can be successfully plated on castaluminum by making use of a preheat to about 570 C.

The applications will be governed by the characteristics obtained in theproduct, such as its mechanical, physical and chemical characteristics.The physical and chemical characteristics, which are innate in thesurfaces of the plated beryllium, are governed also by the assemblypossibilities of such products. The following is typical of thepossibilities:

(a) The possibility to create shapes which are thin, as by folding orembossing the aluminum and beryllium sheets prior to the workingreduction. The possibility of doing such shaping at low temperature,such as between 200-600 C., will be increased from one to three foldwith a layer of plating metal present having a thickness whichcorresponds to 20-50% of the thickness of the beryllium.

(b) The resistance to shock and to abrasion by particles and thesensitivity due to flaws at the surfaces of the beryllium can besuppressed. For this purpose, it is desirable to make use of a ratherthick layer of the plating metal but it is advantageous to use amulti-layer system. Compressor blades are typical of this type ofapplication.

(c) Increased resistance to corrosion by water and by atmosphere issecured. The properties of certain alloys of aluminum can be conferredto the product for use in applications wherein corrosion resistance athigh temperature is important such as in aircraft engines, spacevehicles and nuclear reactors where the structures of this iu ventioncan find application, such as a reflector.

(d) There is the possibility of continuously depositing upon a metalsheet or a composite sheet, a thin layer of the brazing metal, such asan alloy of aluminum with silicon or with zinc, to make it easier tojoin thin strips for electrical leads at low temperature. The presenceof a continuous underlying layer of a metal which is a good conductor,such as aluminum of 99% purity, is desirable to insure that the leadwill separate in whole or in part.

As used herein, the term beryllium is intended to include beryllium andalloys of beryllium.

It will be understood that changes may be made in the details ofconstruction, processes and operations, without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. The metallurgical process for the improvement of the mechanical andphysical properties of beryllium products comprising mechanicallyplating the beryllium with at least one layer of a plastic metalselected from the group consisting of aluminum, magnesium, zinc andantimony at a temperature below 620 C. while mechanically working toeffect a reduction in cross-section of at least 50%.

2. The process as claimed in claim 1 in which the mechanical workingcomprises rolling.

3. The process as claimed in claim mechanical working comprisesspinning.

4. The process as claimed in claim mechanical working comprises drawing.

5. The process as claimed in claim mechanical working comprises forging.

6. The process as claimed in claim 1 in which the mechanical plating iscarried out while at a temperature Within the range of 300-400" C.

7. The process as claimed in claim 1 in which a reduction within therange of 5'0100% in cross-section is obtained during mechanical working.

8. The process as claimed in claim 1 in which the beryllium beforeplating comprises a cast ingot hot worked under a protective atmosphereand then cold worked in the absence of a protective atmosphere to eifecta reduction of 50-l00%.

9. The process as claimed in claim 8 in which the beryllium is pickledbefore mechanical plating.

10. The process as claimed in claim 1 in which the plating is performedon the beryllium by wrapping the beryllium in a thin foil of the plasticmetal and heating to a temperature within the range of 400600 C. beforemechanically working.

11. The process as claimed in claim 1 in which the beryllium is in theform of a thin sheet and in which the plating metal is in the form of athin sheet both of which are folded to form interlayers for themechanically working step.

12. A beryllium product having at least one layer of a plastic metalselected from the group consisting of aluminum, alloys of aluminum,magnesium, Zinc and antimony produced by the method of claim 1.

13. A product produced by the method of claim 1 having a core ofberyllium with at least two layers of a metal selected from the groupconsisting of aluminum, alloys of aluminum, magnesium, zinc andantimony.

14. A product produced by the method of claim 11 1 in which the 1 inwhich the 1 in which the References Cited UNITED STATES PATENTS Davignon29-472.3 'Mooradian 29-472.3 Pflumm et al 29-470.1 Weisse 29-195Whitfield et al. 29-197 Feduska 29-498 6 Feduska et al 29-498 Cowan eta1. 29-197 Bruin 29-49-8 La. -Plante 29-498 5 RICHARD J. H'ERBST,Primary Examiner.

-E. M. COMBS, Assistant Examiner.

US. Cl. X.R.

1. THE METALLURGICAL PROCESS FOR THE IMPROVEMENT OF THE MECHANICAL AND PHYSICAL PROPERTIES OF BERYLLIUM PRODUCTS COMPRISING MECHANICALLY PLATING THE BERYLLIUM WITH AT LEAST ONE LAYER OF A PLASTIC METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM, ZINC AND ANTIMONY AT A TEMPERATURE BELOW 620*C. WHILE MECHANICALLY WORKING TO EFFECT A REDUCTION IN CROSS-SECTION OF AT LEAST 50%. 